1. Field of the Invention
The present invention relates generally to the field of wireless communication, and more particularly to a device and method for transmitting a common channel message in a CDMA (Code Division Multiple Access) communication system.
2. Description of the Related Art
In a communication system based on the TIA/EIA/IS-95 standard, messages are communicated between a base station (BS) and a mobile station (MS) generally on a forward paging channel and a reverse access channel which are common channels before a voice call is set up. For communication with the MS, the BS must transmit a message on the paging channel and receives a response on the access channel. From the mobile""s perspective, for communication with the BS, the MS transmits a message on the access channel and receives a response on the paging channel. There can be a plurality of paging and access channels. Each paging channel is distinguished by a unique Walsh code, and each access channel by a long code generated with an access channel long code mask.
The MS transmits common channel messages on an access channel at a predetermined power level and awaits an acknowledgement from the BS. However, this common channel message transmission is susceptible to message contention if other mobile stations (MSs) are using the same access channel, resulting in a reception failure in the BS. If the MS fails to receive the acknowledgement within a predetermined time, it retransmits the access channel message at a power level incremented by a specified amount and awaits an acknowledgement from the BS.
In the case where the message is too long to be sent at one time, it should be divided into appropriate segments prior to transmission by repeating the above procedure. FIG. 1 is a flowchart illustrating a conventional message exchange when a message cannot be sent at one time and is therefore divided into segments for transmission. In this method, the MS sends a message segment on an access channel and must access the access channel each time to send successive message segments.
In the conventional access channel communication method, if mobile stations (MSs) sharing the same long code simultaneously transmit messages on the access channel, a message contention occurs, resulting in a loss of the messages. This mechanism is generally referred to as contention-based random access.
In the event a message contention should occur on the access channel, the MS should re-attempt to transmit the message on the access channel. In this case, each MS transmits a message on the access channel using the long code commonly shared by the MSes, and if message contention should occur, the MS perceives the occurrence in a predetermined time and re-transmits a message transmission after a randomized time delay.
The MS initially attempts to access the BS, via the access channel, at a predetermined power level. When it fails to receive an acknowledgement from the BS, it performs the next attempt at a power level a specified amount higher than the previous attempt. If repeated attempts to access the access channel result in failures, the procedure starts again at the lowest predetermined power level.
In accordance with the conventional common channel message transmitting method, when the message length is too long to be sent at one time, message segments are transmitted on an access channel in successive time intervals. Therefore, in the situation where different MSs attempt to send messages on the access channel by a shared long code, message contention is a common occurrence, thereby incurring long delays in transmission of an access channel message. Hence, there exists a need for a method to enable a mobile station to rapidly transmit a common channel message.
An object of the present invention, as embodied and broadly described herein, is to provide a device and method for enabling an MS to rapidly transmit a common channel message in a CDMA communication system.
Another object of the present invention is to provide a device and method for enabling an MS to continuously transmit a common channel message on a designated channel if the common channel message is longer than a predetermined length, in a CDMA communication system.
A further object of the present invention is to provide a device and method for enabling an MS to continuously transmit a common channel message on a channel temporarily designated as dedicated in a CDMA communication system.
Still another object of the present invention is to provide a device and method for enabling an MS to transmit the first segment of a common channel message exceeding a predetermined length on a common channel and the following segments on a channel designated by a BS in a CDMA communication system, in order to prevent a message contention for the common channel.
To achieve the above objects, there is provided a common channel message transmitting device and method in a CDMA communication system. In the transmitting method, an MS sends a common channel message with a request for designation of a channel for transmission of a multi-segment common channel message, and a BS sends a response message having an available channel ID for the message received from the MS. Then, the MS analyzes the response message and sends the next message on a channel designated with the assigned channel ID.